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Systems Thinking Case Study #17:
Systemic structures that drive Dengue Fever
Systemic structures that drive Dengue Fever
| HOW COME DENGUE FEVER CASES KEEP COMING BACK DESPITE VIGILANCE AND AWARENESS EFFORTS? |
Local statistics and trends
Some useful links:
Seasonal trends in SEA regions: http://w3.whosea.org/en/Section10/Section332_9482.htm
NUS Study: http://www.ims.nus.edu.sg/Programs/infectiousdiseases/files/markc_1.pdf
Seasonal trends in SEA regions: http://w3.whosea.org/en/Section10/Section332_9482.htm
NUS Study: http://www.ims.nus.edu.sg/Programs/infectiousdiseases/files/markc_1.pdf
| WHAT WOULD IT LOOK LIKE IF WE LEARN TO APPLY THESE STRATEGIES? WHAT MIGHT MAKE IT DIFFICULT OR GET IN THE WAY OF MAKING THESE HAPPEN? WHAT KEEPS OUR CONVERSATIONS LIKE THESE AND IS MAKING IT DIFFICULT TO SEE THESE STRUCTURES? Click here to share your thoughts, comments and reactions |
In Singapore, larger outbreaks of dengue tend to occur every five to six years. Since
the early 1990s, dengue incidence during major outbreaks has been rising steadily in
country. In 2004, 9459 cases and eight deaths were reported. This is the highest
number of cases reported during the last 15 years, and almost twice as many cases
as during the 1998 epidemic.
Control of Ae. aegypti and Ae. albopictus is largely done through source reduction.
Other strategies involve health education, application of public health regulations, and
chemical control.
GLOBAL TRENDS:
Dengue is found in tropical and sub-tropical regions around the world, predominantly
in urban and semi-urban areas. It has been estimated that a total of 3.5 million
people residing mainly in urban areas with a population density of greater than 250
per square kilometre are at great risk of dengue fever (DF) and dengue haemorrhagic
fever (DHF). The epidemic nature of the disease, the high prevalence among the
poorest urban populations, the high morbidity and mortality among children, and the
increasing geographical spread of the disease to rural villages pose a great challenge
to the public health.
THE ROOT OF THE CAUSE:
Dengue is a mosquito-borne infection which in recent years has become a major
international public health concern.
Dengue haemorrhagic fever (DHF), a potentially lethal complication, was first
recognized in the 1950s during the dengue epidemics in the Philippines and Thailand,
but today DHF affects most Asian countries and has become a leading cause of
hospitalisation and death among children in several of them.
Everytime we learn something, something new comes up,'' said Yaacob Ibrahim, the
minister in charge of a high-level committee on dengue in Singapore.
And for a disease that afflicts an estimated 50 million worldwide annually, according to
the World Health Organisation, there remains no drug or known remedy.
the early 1990s, dengue incidence during major outbreaks has been rising steadily in
country. In 2004, 9459 cases and eight deaths were reported. This is the highest
number of cases reported during the last 15 years, and almost twice as many cases
as during the 1998 epidemic.
Control of Ae. aegypti and Ae. albopictus is largely done through source reduction.
Other strategies involve health education, application of public health regulations, and
chemical control.
GLOBAL TRENDS:
Dengue is found in tropical and sub-tropical regions around the world, predominantly
in urban and semi-urban areas. It has been estimated that a total of 3.5 million
people residing mainly in urban areas with a population density of greater than 250
per square kilometre are at great risk of dengue fever (DF) and dengue haemorrhagic
fever (DHF). The epidemic nature of the disease, the high prevalence among the
poorest urban populations, the high morbidity and mortality among children, and the
increasing geographical spread of the disease to rural villages pose a great challenge
to the public health.
- The global prevalence of dengue has grown dramatically in recent decades.
The disease is now endemic in more than 100 countries in Africa, the Americas,
the Eastern Mediterranean, South-east Asia and the Western Pacific. South-
east Asia and the Western Pacific are most seriously affected. Before 1970 only
nine countries had experienced DHF epidemics, a number that had increased
more than four-fold by 1995.
- Some 2500 million people -- two fifths of the world's population -- are now at
risk from dengue. WHO currently estimates there may be 50 million cases of
dengue infection worldwide every year.
- In 2001 alone, there were more than 609 000 reported cases of dengue in the
Americas, of which 15 000 cases were DHF. This is greater than double the
number of dengue cases which were recorded in the same region in 1995.
- Not only is the number of cases increasing as the disease is spreading to new
areas, but explosive outbreaks are occurring. In 2001, Brazil reported over
390 000 cases including more than 670 cases of DHF.
THE ROOT OF THE CAUSE:
Dengue is a mosquito-borne infection which in recent years has become a major
international public health concern.
Dengue haemorrhagic fever (DHF), a potentially lethal complication, was first
recognized in the 1950s during the dengue epidemics in the Philippines and Thailand,
but today DHF affects most Asian countries and has become a leading cause of
hospitalisation and death among children in several of them.
- Viral hemorrhagic fevers (VHFs) refer to a group of illnesses that are caused by
several distinct families of viruses. In general, the term "viral hemorrhagic
fever" is used to describe a severe multisystem syndrome (multisystem in that
multiple organ systems in the body are affected). Characteristically, the overall
vascular system is damaged, and the body's ability to regulate itself is
impaired. These symptoms are often accompanied by hemorrhage (bleeding);
however, the bleeding is itself rarely life-threatening. While some types of
hemorrhagic fever viruses can cause relatively mild illnesses, many of these
viruses cause severe, life-threatening disease.
- Viruses associated with most VHFs are zoonotic. This means that these viruses
naturally reside in an animal reservoir host or arthropod vector. They are
totally dependent on their hosts for replication and overall survival. For the
most part, rodents and arthropods are the main reservoirs for viruses causing
VHFs. The multimammate rat, cotton rat, deer mouse, house mouse, and
other field rodents are examples of reservoir hosts. Arthropod ticks and
mosquitoes serve as vectors for some of the illnesses. However, the hosts of
some viruses remain unknown -- Ebola and Marburg viruses are well-known
examples.
- Viruses causing hemorrhagic fever are initially transmitted to humans when the
activities of infected reservoir hosts or vectors and humans overlap. The
viruses carried in rodent reservoirs are transmitted when humans have contact
with urine, fecal matter, saliva, or other body excretions from infected rodents.
The viruses associated with arthropod vectors are spread most often when the
vector mosquito or tick bites a human, or when a human crushes a tick.
However, some of these vectors may spread virus to animals, livestock, for
example. Humans then become infected when they care for or slaughter the
animals.
- Some viruses that cause hemorrhagic fever can spread from one person to
another, once an initial person has become infected. Ebola, Marburg, Lassa and
Crimean-Congo hemorrhagic fever viruses are examples. This type of
secondary transmission of the virus can occur directly, through close contact
with infected people or their body fluids. It can also occur indirectly, through
contact with objects contaminated with infected body fluids. For example,
contaminated syringes and needles have played an important role in spreading
infection in outbreaks of Ebola hemorrhagic fever and Lassa fever.
- Takeda et al. isolated TBE virus from Ixodes ovatus ticks collected in the region
and demonstrated that the isolated viruses were antigenically close to RSSE
virus (12). They also showed that captured rodents had antibodies to TBE
virus and that the viruses isolated from the rodents were also antigenically
close to RSSE virus (13). These reports indicate that the TBE virus endemic in
Hokkaido is closely related to RSSE viruses. Further studies are necessary for
understanding the ecologic features of TBE virus in other islands of Japan.
- The spread of dengue is attributed to expanding geographic distribution of the
four dengue viruses and of their mosquito vectors, the most important of
which is the predominantly urban species Aedes aegypti. A rapid rise in urban
populations is bringing ever greater numbers of people into contact with this
vector, especially in areas that are favourable for mosquito breeding, e.g.
where household water storage is common and where solid waste disposal
services are inadequate
Everytime we learn something, something new comes up,'' said Yaacob Ibrahim, the
minister in charge of a high-level committee on dengue in Singapore.
And for a disease that afflicts an estimated 50 million worldwide annually, according to
the World Health Organisation, there remains no drug or known remedy.
INHERENT SYSTEMIC STRUCTURE: FIXES THAT BACKFIRE |
SUCCESS TO THE SUCCESSFUL:
ys in the food have access to yextent to
which the predators extent to which
the predators survive.
dators survive.
survive.
ys in the food have access to yextent to
which the predators extent to which
the predators survive.
dators survive.
survive.
- So for example, the closure of
drains has effectively cut off the
food-chain for the frogs (access
to most insects including
mosquitoes, leading to a rise of
the mosquito population and
eventual decline of the frog
population, the natural preys of
mosquitoes)
DRIFTING GOALS:
- The level of tolerance for rats in
Asian societies (we don't deem
rats as completely intolerable as
most Western societies do
because of the association of rats
in our traditions and myths) and
cities that are expanding rapidly
(we don't have time to deal with
rats!). - In some areas, rats are regarded
for its virtues of shrewdness and
resourcefulness ... hmm .... - In the West, if someone says
'You are rat', that is the lowest
form of attribution anyone can
accord on another! It is
despicable!
FIXES THAT BACKFIRE (see
graphs above):
graphs above):
- When we pay attention to part
of the structure and not see the
whole structure completely, we
tend to focus on causes close in
time and space. - The deeper causes (such as the
proliferation of rats and the
access of mosquitoes to the rats)
are not as apparent and these
parts of the system, continue to
prevail. - These underlying causes come
back in a few years' time and
cause an epidemic to upsurge!